Distinct TCRAV and TCRBV repertoire and CDR3 sequence of T lymphocytes clonally expanded in blood and GVHD lesions after human allogeneic bone marrow transplantation

Tissue-specific features of the T cell repertoire after allogeneic hematopoietic cell transplantation in human and mouse

T cells are the central drivers of many inflammatory diseases, but the repertoire of tissue-resident T cells at sites of pathology in human organs remains poorly understood. We examined the site-specificity of T cell receptor (TCR) repertoires across tissues (5 to 18 tissues per patient) in prospectively collected autopsies of patients with and without graft-versus-host disease (GVHD), a potentially lethal tissue-targeting complication of allogeneic hematopoietic cell transplantation, and in mouse models of GVHD. Anatomic similarity between tissues was a key determinant of TCR repertoire composition within patients, independent of disease or transplant status. The T cells recovered from peripheral blood and spleens in patients and mice captured a limited portion of the TCR repertoire detected in tissues. Whereas few T cell clones were shared across patients, motif-based clustering revealed shared repertoire signatures across patients in a tissue-specific fashion. T cells at disease sites had a tissue-resident phenotype and were of donor origin based on single-cell chimerism analysis. These data demonstrate the complex composition of T cell populations that persist in human tissues at the end stage of an inflammatory disorder after lymphocyte-directed therapy. These findings also underscore the importance of studying T cell in tissues rather than blood for tissue-based pathologies and suggest the tissue-specific nature of both the endogenous and posttransplant T cell landscape.

Potential of TCR sequencing in graft-versus-host disease

Graft-versus-host disease (GvHD) remains one of the major complications following allogeneic haematopoietic stem cell transplantation (allo-HSCT). GvHD can occur in almost every tissue, with the skin, liver, and intestines being the mainly affected organs. T cells are implicated in initiating GvHD. T cells identify a broad range of antigens and mediate the immune response through receptors on their surfaces (T cell receptors, TCRs). The composition of TCRs within a T cell population defines the TCR repertoire of an individual, and this repertoire represents exposure to self and non-self proteins. Monitoring the changes in the TCR repertoire using TCR sequencing can provide an indication of the dynamics of a T cell population. Monitoring the frequency and specificities of specific TCR clonotypes longitudinally in different conditions and specimens (peripheral blood, GvHD-affected tissue samples) can provide insights into factors modulating immune reactions following allogeneic transplantation and will help to understand the underlying mechanisms mediating GvHD. This review provides insights into current studies of the TCR repertoire in GvHD and potential future clinical implications of TCR sequencing.

Analysis of T-Cell Receptor Repertoire in Transplantation: Fingerprint of T Cell-mediated Alloresponse

T cells play a key role in determining allograft function by mediating allogeneic immune responses to cause rejection, and recent work pointed their role in mediating tolerance in transplantation. The unique T-cell receptor (TCR) expressed on the surface of each T cell determines the antigen specificity of the cell and can be the specific fingerprint for identifying and monitoring. Next-generation sequencing (NGS) techniques provide powerful tools for deep and high-throughput TCR profiling, and facilitate to depict the entire T cell repertoire profile and trace antigen-specific T cells in circulation and local tissues. Tailing T cell transcriptomes and TCR sequences at the single cell level provides a full landscape of alloreactive T-cell clones development and biofunction in alloresponse. Here, we review the recent advances in TCR sequencing techniques and computational tools, as well as the recent discovery in overall TCR profile and antigen-specific T cells tracking in transplantation. We further discuss the challenges and potential of using TCR sequencing-based assays to profile alloreactive TCR repertoire as the fingerprint for immune monitoring and prediction of rejection and tolerance.

Analysis of the CDR3 length repertoire and the diversity of T cell receptor α and β chains in swine CD4+ and CD8+ T lymphocytes

The T cell receptor (TCR) is a complex heterodimer that recognizes fragments of antigens as peptides and binds to major histocompatibility complex molecules. The TCR α and β chains possess three hypervariable regions termed complementarity determining regions (CDR1, 2 and 3). CDR3 is responsible for recognizing processed antigen peptides. Immunoscope spectratyping is a simple technique for analyzing CDR3 polymorphisms and sequence length diversity, in order to investigate T cell function and the pattern of TCR utilization. The present study employed this technique to analyze CDR3 polymorphisms and the sequence length diversity of TCR α and β chains in porcine CD4⁺ and CD8⁺ T cells. Polymerase chain reaction products of 19 TCR α variable regions (AV) and 20 TCR β variable regions (BV) gene families obtained from the CD4⁺ and CD8⁺ T cells revealed a clear band following separation by 1.5% agarose gel electrophoresis, and each family exhibited >8 bands following separation by 6% sequencing gel electrophoresis. CDR3 spectratyping of all identified TCR AV and BV gene families in the sorted CD4⁺ and CD8⁺ T cells by GeneScan, demonstrated a standard Gaussian distribution with >8 peaks. CDR3 in CD4⁺ and CD8⁺ T cells demonstrated different expression patterns. The majority of CDR3 recombined in frame and the results revealed that there were 10 and 14 amino acid discrepancies between the longest and shortest CDR3 lengths in specific TCR AV and TCR BV gene families, respectively. The results demonstrated that CDR3 polymorphism and length diversity demonstrated different expression and utilization patterns in CD4⁺ and CD8⁺ T cells. These results may facilitate future research investigating the porcine TCR CDR3 gene repertoire as well as the functional complexity and specificity of the TCR molecule.

Clinical Implications of T Cell Receptor Repertoire Analysis after Allogeneic Stem Cell Transplantation

Stem cell transplantation (SCT) constitutes a major challenge to the immune system. Long-term impairment of immunity against various common infectious stimuli leads to increased susceptibility to infectious diseases; in contrast, an immune response against the recipient may cause the devastating graft-versus-host disease (GvHD). Recovery of the immune system (both qualitative and quantitative) after SCT is perhaps the most important factor in determining the clinical outcome. Consequently, immune reconstitution has been extensively studied using different approaches, including quantitative analysis of immune cells as well as their phenotypic characterization. Analysis of diversity and clonality is an important tool in determining competence of the immune system, assuming that a broad diversity assures efficient response to different stimuli and clonal dominance reflects ongoing, potentially relevant immune responses. Detailed analysis of the immune repertoire through the flow cytometric and molecular study of the T cell receptor repertoire has been applied to gain quantitative and qualitative insights about the T cell immune competence and responsiveness. After SCT, a contraction of the T cell pool and a reduction in T cell receptor diversity is clearly associated with clinical immunodeficiency. Reconstitution of the immune system is often characterized by dominance of oligoclonal T cell populations, reflecting specific antigen-driven immune responses. Detailed characterization of T lymphocytes by T cell receptor analysis is possible, and may lead to the identification of individual clones involved in specific immune reactions, such as alloresponses in GvHD, the closely related graft-versus-leukemia effect and opportunistic viral agents such as CMV or EBV.

TRBV kinetics and its association with HLA disparity and aGVHD following allogeneic hematopoietic stem cell transplantation

INTRODUCTION

The relative expression of T cell receptor (TCR) beta variable (TRBV) and TCR diversity was compared between recipients receiving human leukocyte antigen (HLA)-mismatched transplants and those receiving HLA-matched transplants, using granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood stem cells and bone marrow as grafts.

METHODS

The kinetics of the relative expression of TRBV family members were analyzed using real-time quantitative PCR. Additionally, the association of TRBV clonotype with acute graft-versus-host disease (aGVHD) was determined by cloning and sequence analysis of the CDR3 region.

RESULTS

The TCR diversity in recipients receiving HLA-mismatched transplants was significantly lower than in those receiving HLA-matched transplants at 1 month and 2 months after hematopoietic stem cell transplantation (HSCT) (both P < 0.05). However, these differences disappeared 3 months after transplantation. The relative expression of TRBV27 (n = 7 recipients) at the onset of aGVHD was higher than in corresponding donors (P = 0.025), but no significant differences were observed between recipients lacking aGVHD and their donors at serial time points after HSCT.

CONCLUSION

Our results suggest that HLA disparity may affect the relative expression of TRBV in the early phase after transplantation, and TRBV27 may be associated with the onset of aGVHD.

Alloimmune response results in expansion of autoreactive donor CD4+ T cells in transplants that can mediate chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is considered an autoimmune-like disease mediated by donor CD4(+) T cells, but the origin of the autoreactive T cells is still controversial. In this article, we report that the transplantation of DBA/2 donor spleen cells into thymectomized MHC-matched allogeneic BALB/c recipients induced autoimmune-like cGVHD, although not in control syngeneic DBA/2 recipients. The donor-type CD4(+) T cells from the former but not the latter recipients induced autoimmune-like manifestations in secondary allogeneic BALB/c as well as syngeneic DBA/2 recipients. Transfer of donor-type CD4(+) T cells from secondary DBA/2 recipients with disease into syngeneic donor-type or allogeneic host-type tertiary recipients propagated autoimmune-like manifestations in both. Furthermore, TCR spectratyping revealed that the clonal expansion of the autoreactive CD4(+) T cells in cGVHD recipients was initiated by an alloimmune response. Finally, hybridoma CD4(+) T clones derived from DBA/2 recipients with disease proliferated similarly in response to stimulation by syngeneic donor-type or allogeneic host-type dendritic cells. These results demonstrate that the autoimmune-like manifestations in cGVHD can be mediated by a population of donor CD4(+) T cells in transplants that simultaneously recognize Ags presented by both donor and host APCs.

Accumulation of autoreactive effector T cells and allo-specific regulatory T cells in the pancreas allograft of a type 1 diabetic recipient

AIMS/HYPOTHESIS

Simultaneous kidney-pancreas transplantation is an established treatment for patients with type 1 diabetes and end-stage renal failure, even though restored beta cell function may become affected by recurrent islet autoimmunity or graft rejection. We characterised infiltrating lymphocytes isolated from a pancreatic graft with normal endocrine function in a kidney-pancreas recipient with type 1 diabetes.

METHODS

The pancreas graft was removed due to recurrent graft pancreatitis of unknown cause. Pancreas-infiltrating lymphocytes and peripheral blood mononuclear cells (PBMC) were isolated and characterised phenotypically and functionally.

RESULTS

Compared with PBMC, pancreas-infiltrating lymphocytes exhibited a distinct activation/memory phenotype and T cell receptor profile that were indicative of selective infiltration of the pancreas. Islet autoreactive CD8(+) T cells could be detected in the pancreas and were increased in frequency compared with PBMC. Additionally, an augmentation of CD8(+) CD28(-) regulatory T cells was observed in the pancreas; these induced expression of the inhibitory receptor immunoglobulin-like transcript-3 on antigen-presenting cells in a donor HLA class I-specific manner.

CONCLUSIONS/INTERPRETATION

These data demonstrate the simultaneous presence of regulatory and effector T cells in the pancreas allograft of a recipient with type 1 diabetes. They also indicate that circulating islet autoreactive T cells may reflect immunological processes in pancreatic tissue, even though their frequency in the periphery may lead to underestimation of their presence in the pancreas. Additional specificities were also present in the pancreas that were undetectable in the circulation.

TCR spectratyping revealed T lymphocytes associated with graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Clonal expansion of T cells after allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been observed, but their characteristics remain to be fully elucidated. We report here that CD8(+) T cells were the dominant T lymphocytes seen and T-cell repertoire diversity decreased dramatically during the first 3 months after allo-HSCT. Patients with GVHD grade II - IV had significantly lower T-cell repertoire diversity compared with non-GVHD patients. TCR beta variable gene (TCRBV) subfamily 8, 5.1, 5.2, 4, and 13 were the five most frequently expanded subfamilies among these patients. Among the 49 over-expanded clones identified, clonotype "TCR3-5" and "TCR18-5" were isolated from four patients with HLA-A2 allele and skin GVHD. Their frequencies correlated well with skin symptoms (i.e. rash). Moreover, they were detected in donors but not detected in recipients before transplantation. Lastly, three common TCRBV CDR3 motifs shared by T cells related with GVHD were discovered: TGDS, GLAG, and GGG. These findings suggest that TCR spectratyping is helpful for revealing GVHD-related T cells and may have utility in early diagnosis.

Molecular analysis of alloreactive CTL post-hemopoietic stem cell transplantation

The development of laboratory tests for the diagnosis and monitoring of graft-vs-host disease (GVHD) is hampered by a lack of knowledge of minor histocompatibility Ags triggering alloresponses. We hypothesized that the unique molecular structure of the TCR could be used as a marker for the unidentified Ags and exploited for molecular monitoring of GVHD posttransplant. To identify alloreactive T cell clones, we performed in vitro allostimulation cultures for a cohort of patients undergoing hemopoietic stem cell transplantation and determined the sequence of the CDR3 of immunodominant alloreactive clones; 10 corresponding clonotypes restricted to activated T cells were identified. As an alternative method for the identification of alloreactive clones, molecular TCR analysis was applied to biopsies of GVHD-affected tissues. Culture- and biopsy-derived clonotypes were used to design sequence-specific quantitative PCR assays to monitor the levels of putative allospecific clonotypes in posttransplant blood samples and subsequent biopsies. Because of the rational design of the methods used to identify immunodominant clonotypes, we were able to follow the behavior of potentially GVHD-specific T cells during the transplant course. Based on our results, we conclude that molecular T cell diagnostics can be a powerful tool for monitoring immune responses posttransplantation.

Patterns of T-cell reconstitution by assessment of T-cell receptor excision circle and T-cell receptor clonal repertoire after allogeneic hematopoietic stem cell transplantation in leukemia patients ? a study in Chinese patients

OBJECTIVE

Successful allogeneic hematopoietic stem cell transplantation (HSCT) requires reconstitution normal T-cell immunity. Measurement of T-cell receptor excision circles (TRECs) and T-cell receptor beta (TCRBV) CDR3 repertoire is a means of quantifying recent thymic T-cell production and reflecting antigen-specific T-cell clones proliferation.

METHODS

We used real-time quantitative PCR to detect TRECs from 43 Chinese patients who underwent three kind of allo-HSCT without T-cell depletion. RT-PCR was performed to amplify 24 subfamily genes of TCRBV in 24 patients of them.

RESULTS

For haploidentical-D group, the TRECs numbers were lower up to 24 months. For matched-sibling donor (MSD) group, the recovery of TRECs was faster than those of other two groups. TRECs values in matched-unrelated donor (MUD) were in the middle. During 2-19 months after transplantation, there were 6-16 BV subfamilies expressed and 33-48% of them were polyclones. The usage rate of TCRBV and percentage of polyclones in haploidentical-D were less than those of other two groups. Twenty-three CDR3 molecules were obtained from nine patients who were potentially associated with GVHD or CMV infection.

CONCLUSIONS

Analyzing the changes of TCRBV repertoire and measuring TRECs during immune reconstitution would be useful to determine the host's current immune status and ability of T-cell immune reconstitution and also to find antigen-specific T-cell clones in the three kinds of HSCT.

Allorecognition and the alloresponse: clinical implications

The artificial transfer of tissues or cells between genetically diverse individuals elicits an immune response that is adaptive and specific. This response is orchestrated by T lymphocytes that are recognizing, amongst others, major histocompatibility complex (MHC) molecules expressed on the surface of the transferred cells. Three pathways of recognition are described: direct, indirect and semi-direct. The sets of antigens that are recognized in this setting are also discussed, namely, MHC protein products, the MHC class I-related chain (MIC) system, minor histocompatibility antigens and natural killer cell receptor ligands. The end product of the effector responses are hyperacute, acute and chronic rejection. Special circumstances surround the situation of pregnancy and bone marrow transplantation because in the latter, the transferred cells are the ones originating the immune response, not the host. As the understanding of these processes improves, the ability to generate clinically viable immunotherapies will increase.

Expression of CD27 on Peripheral CD4 + T-Lymphocytes Correlates with the Development of Severe Acute Graft-versus-Host Disease after Allogeneic Bone Marrow Transplantation

Allogeneic immune responses during hematopoietic reconstitution play central roles in beneficial and adverse effects after allogeneic bone marrow transplantation (allo-BMT). Appropriate regulation of the immune responses might improve the outcome of allo-BMT. However, a useful marker for monitoring allogeneic immune responses remains to be established. We enrolled 22 consecutive patients who underwent myeloablative allo-BMT between March 2002 and March 2006 and examined the relationship between CD27 expression on peripheral blood T-lymphocytes, a possible marker for naive/effector phenotypes, and clinical events, especially acute graft-versus-host disease (aGVHD). In 8 patients with aGVHD of grades II to IV, the CD27+/CD27- ratios of CD4+ (but not CD8+) T-lymphocytes were significantly higher after allo-BMT, even at day 21, than the ratios in patients with aGVHD of grade 0 or I and remained high after day 21. In contrast, the ratios were low after day 21 following allo-BMT in 14 patients with aGVHD of grade 0 or I. Moreover, the clinical analysis suggested a relationship between the ratio and aGVHD grade. Thus, we showed that the CD27+/CD27- ratio in CD4+ T-lymphocytes may have value in predicting the development of severe aGVHD and may correlate with clinical symptoms of aGVHD.

T-cell receptor Valpha spectratype analysis of a CD4-mediated T-cell response against minor histocompatibility antigens involved in severe graft-versus-host disease

Although CD4(+) T cells can have an important role in mediating lethal graft-versus-host disease (GVHD) directed to multiple minor histocompatibility antigens (miHA) after bone marrow transplantation, their precise characterization and effector function remains elusive. In this regard, T cell receptor (TCR) Vbeta spectratype analysis has been a powerful tool for identifying donor CD4(+) T cell populations expanding to host miHA after bone marrow transplantation in the major histocompatibility complex-matched C57BL/6 (B6) --> C.B10-H2(b) (BALB.B) model of lethal GVHD. Removal of all of the Vbeta(+) T cell families containing these responding cells from the donor inoculum has proven to be an effective means of preventing the development of GVHD. Previous studies have also found that of the 11 miHA-responsive B6 CD4(+) Vbeta(+) T cell families, transplantation of Vbeta2(+) and Vbeta11(+) T cells together into lethally irradiated BALB.B mice appeared to be primarily responsible for the severity of resultant GVHD. Further focusing on these critical CD4 responses, in this study we demonstrate that B6 CD4(+)Vbeta11(+) T cells alone can induce lethal GVHD in BALB.B recipients. In addition, immunohistochemical staining of host lingual and intestinal epithelial tissues supported the capacity of Vbeta11(+) T cells to infiltrate typical GVHD-associated target areas. To further characterize the specific CD4(+)Vbeta11(+) T cells involved in this anti-miHA response, TCR Valpha spectratype analysis was performed and indicated that 6 Valpha chains were used by this reactive population. These results provide further evidence that a restricted repertoire of T cell specificities, presumably recognizing a correspondingly low number of miHA, is sufficient for the induction of severe GVHD.

Pathologic clonal cytotoxic T-cell responses: nonrandom nature of the T-cell–receptor restriction in large granular lymphocyte leukemia

T-cell large granular lymphocyte (T-LGL) leukemia is a clonal lymphoproliferation of cytotoxic T cells (CTLs) associated with cytopenias. T-LGL proliferation seems to be triggered/sustained by antigenic drive; it is likely that hematopoietic progenitors are the targets in this process. The antigen-specific portion of the T-cell receptor (TCR), the variable beta (VB)–chain complementarity-determining region 3 (CDR3), can serve as a molecular signature (clonotype) of a T-cell clone. We hypothesized that clonal CTL proliferation develops not randomly but in the context of an autoimmune response. We identified the clonotypic sequence of T-LGL clones in 60 patients, including 56 with known T-LGL and 4 with unspecified neutropenia. Our method also allowed for the measurement of clonal frequencies; a decrease in or loss of the pathogenic clonotype and restoration of the TCR repertoire was found after hematologic remission. We identified 2 patients with identical immunodominant CDR3 sequence. Moreover, we found similarity between multiple immunodominant clonotypes and codominant as well as a nonexpanded, “supporting” clonotypes. The data suggest a nonrandom clonal selection in T-LGL, possibly driven by a common antigen. In contrast, the physiologic clonal CTL repertoire is highly diverse and we were not able to detect any significant clonal sharing in 26 healthy controls.

An improved methodology to detect human T cell receptor beta variable family gene expression patterns

Comprehensive gene expression analysis of the T cell receptor repertoire of an individual can be very useful in evaluating the immune response in a variety of conditions. Antibody-based analysis methods can detect approximately 60% of the human T cell receptor beta variable (TCRBV) proteins, while gene expression analysis, primarily through employment of the polymerase chain reaction (PCR), has had somewhat greater success in the detection of additional TCRBV families. Many of these previous PCR methods, however, have been unable to detect all 91 alleles of the human TCRBV genes. This is primarily due to either deficiencies in the amplification of all of the variable beta families, subfamilies, and alleles, or the prior lack of a systematic classification of the TCR variable family gene segment sequences. We describe here a real-time reverse transcription polymerase chain reaction-based method, which allows efficient automation and integration of amplification, detection, and analysis with sequence-specific detection of all T cell receptor beta variable gene families, subfamilies, and alleles. This method, which in itself contributes significant improvements over existing technologies through its comprehensiveness and efficiency, also functions independently of variables such as sample source and sample processing and has the ability to run on multiple real-time PCR platforms, affording one the implementation of personal preferences.

Efficient identification of T-cell clones associated with graft-versus-host disease in target tissue allows for subsequent detection in peripheral blood

Graft-versus-host disease (GVHD) causes severe morbidity and mortality in allogeneic haematopoietic stem cell transplantation (HSCT) because of destruction of recipient tissues by donor alloreactive T cells. We hypothesized that GVHD-specific T-cell clones are expanded within affected tissue of HSCT patients and can also be detected in blood at the time of active disease. A multiplex polymerase chain reaction (PCR) was used to amplify T-cell receptor (TCR) variable beta (VB) chain rearrangements in skin biopsies from eight allogeneic HSCT patients. Molecular analysis of the complementarity-determining region 3 (CDR3) of amplified products defined expanded, potentially disease-associated 'clonotypes' and enabled the design of clonotype-specific PCR assays. We detected immunodominant clones in seven of eight GVHD-positive skin biopsies. In serial skin biopsies from the same patient, the identical clone was found in each biopsy. In a patient who underwent two successive HSCTs from different donors, distinct clones were identified for each engraftment. Using clonotypic PCR assays, individual tissue-derived clones could be identified in peripheral blood samples obtained during active GVHD. We hypothesize that clonotypic sequences derived from target tissue can serve as markers for GVHD and may have utility in diagnosis and monitoring response to therapy, as well as enable future therapies targeted against pathogenic clones.

T cell immunity and graft-versus-host disease (GVHD)

Graft-versus-host disease (GVHD), induced by the reaction of donor T cells to recipient histoincompatible antigens, is a serious complication of allogeneic bone marrow transplantation (BMT), resulting in considerable morbidity and mortality. In MHC-disparate BMT, donor T cells directly react with major histocompatibility complex (MHC) antigens, while in MHC-matched BMT, T cells react with minor histocompatibility antigens (miHA) presented by shared MHC molecules. Clinically, acute and chronic GVHD can be distinguished on the basis of the time of onset, clinical manifestations and distinct pathobiological mechanisms. Acute GVHD usually occurs within 2 to 6 weeks following allogeneic BMT and primarily affects the skin, liver and the gastrointestinal tract with T cell infiltration of the epithelia of the skin, mucous membranes, bile ducts and gut. In addition, hair follicle cells, airways, bone marrow, and a variety of other tissue systems can be involved. Acute GVHD occurs in up to 50% of allogeneic HLA-matched and 70% of HLA-disparate BMT recipients despite prophylactic immunosuppressive drugs. Chronic GVHD involves a wider range of organs and clinical manifestations include scleroderma, liver failure, immune complex disease, glomerulonephritis, and autoantibody formation.

Molecular TCR diagnostics can be used to identify shared clonotypes after allogeneic hematopoietic stem cell transplantation

OBJECTIVE

In allogeneic hematopoietic stem cell (HSCT) transplantation, recovery of the T cell receptor (TCR) repertoire depends upon the composition of the graft and is modulated by peri-transplant immunosuppression, viral infections, and graft-vs-host disease (GVHD). We hypothesized that after allogeneic HSCT, molecular analysis of the TCR repertoire can be used to identify and quantitate immunodominant T cell clones that may play a role in GVHD or other clinical events.

METHODS

We utilized a rational strategy for the analysis of the expanded CTL clones. First, we studied the VB spectrum in a cohort of patients who had received either matched sibling or unrelated donor grafts. The CDR3 sequences of immunodominant clones were identified and clonotypic PCR and sequencing was applied to determine the level of clonotype sharing.

RESULTS

Significant expansions of VB families were observed following transplantations; 61% were oligo/monoclonal. Immunodeficiency was reflected by depletion of multiple VB families from both the CD8 and CD4 repertoires. The level of sharing varied between clonotypes, suggesting that some antigens have a more "public" spectrum while others are restricted to specific patients. Immunodominant CDR3 sequences common to allogeneic HSCT, healthy controls, and other conditions were identified.

CONCLUSION

The clonotypes of expanded CTL clones may reflect responses to alloantigens (e.g., in correlation with clinical GVHD) or pathogens. In the future, molecular T cell diagnostics may become a powerful clinical tool in transplantation to monitor disease and to direct treatment.

The presence and longevity of peripherally expanded donor-derived TCRalphabeta+ mature T lymphocyte clones after allogeneic bone marrow transplantation for adult myeloid leukemias

There are two major pathways for T-cell regeneration after allogeneic bone marrow transplantation; thymus-dependent T-cell differentiation of T-cell progenitors, and peripheral expansion of mature T cells in the graft. In order to learn to what extent the peripheral expansion of donor-derived mature T lymphocytes contributes to reconstitution of the TCRalphabeta+ T-cell repertoire after allogeneic bone marrow transplantation for adult myeloid leukemias, we pursued the fate of donor-derived T-cell clones using the amino-acid sequences of the complementarity-determining region 3 (CDR3) of the TCR-beta chain as a clonal marker. Clonal expansion of TCRalphabeta+ T lymphocytes with specific TCRBV subfamilies was identified in donor blood. Identical T-cell clones were not found in blood from recipients before transplantation. The donor-derived T-cell clones were identified in the circulating blood from recipients a few months after allogeneic bone marrow transplantation, and they remained in the blood for 18 months after transplant in two recipients, and for 56 months in one. These results suggest that the peripheral expansion of mature T lymphocytes in the graft makes a significant contribution to post-transplant T-cell regeneration during the early period of transplantation in humans, and that mature T cells can survive in recipients for several years. Further investigation will be required to explore which antigens drive the expansion of T-cell clones in donors and recipients, and the mechanisms of maintaining homeostatic balance between the thymus-dependent pathway and the peripheral expansion of mature T cells in post-transplant T-cell regeneration.